Field of the Invention
One or more embodiments relate to a positive active material, a method of preparing the same, a positive electrode for a lithium secondary battery including the positive active material, and a lithium secondary battery including the same, and more particularly to a positive active material that has a decreased amount of Li-containing impurities that remain on a surface of a lithium transition metal composite oxide to decrease an amount of gas generation and has improved lifespan properties, a method of preparing the same, a positive electrode for a lithium secondary battery including the positive active material, and a lithium secondary battery including the same.
Description of the Related Art
Lithium secondary batteries used in mobile electronic devices for information communication, such as personal digital assistants (PDAs), mobile phones, and notebook computers, or in electric bicycles and electric vehicles have discharge voltages that are at least twice as high as conventional batteries, and thus, the lithium secondary batteries have large energy densities.
The lithium secondary batteries produce electrical energy through a redox reaction that occurs when lithium ions are intercalated and de-intercalated from a positive electrode and a negative electrode, and an organic electrolyte or a polymer electrolyte is charged between the positive electrode and the negative electrode including active materials that are capable of intercalation and de-intercalation of lithium ions.
The positive active materials of the lithium secondary batteries include lithium transition metal composite oxides including a transition metal and a lithium having a structure capable of intercalation of lithium ions, and examples of the positive active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or lithium nickel cobalt manganese oxide (for example, Li[NiCoMn]O2, Li[Ni1-x-yCoxMy]O2).
However, the lithium transition metal composite oxide gradually has a decreasing calcination temperature as increasing in an amount of nickel in the lithium transition metal composite oxide, such that amounts of Li-containing impurities, such as Li2CO3 and LiOH, increase on a surface of the positive active material, which decomposes during a charge or reacts with an electrolyte to generate gases such as CO2 to deteriorate lifespan properties.
Accordingly, there is a need for decreasing the amounts of Li-containing impurities, such as Li2CO3 and LiOH, that remain on the surface of the positive active material and solving the problem through a simple and cost-effective method.